Recently, gas laser oscillators are being reduced in size. To achieve this goal, the exciting frequency for a discharging gas laser has gradually reached higher frequencies. Hitherto, to supply the frequency for such gas laser oscillation, high frequency power sources of 100 kHz to scores of megahertz have been used. However, to reduce the size, problems of price and control performance occur. To solve these problems, various studies have been made on the microwave excited gas laser oscillator (herein after called MEGLO) for exciting by discharging laser gas by microwave.
FIG. 6 is a schematic diagram for explaining a constitution of a conventional MEGLO, and it is described below while referring to the drawing.
A microwave power source (hereinafter called power source) 4 is a switching power source of about 20 kHz, and a high voltage is applied so that a magnetron 1 may produce a microwave. The microwave emitted from the magnetron 1 is injected through a waveguide 2 into a discharge area 10 which is part of a discharge tube 3 in which laser gas flows. In the discharge area 10, the laser gas is discharged and excited by the microwave. The excited and generated laser beam is amplified in a laser resonator composed of an output mirror 8 which is a partial reflector and a total reflector 9. Part of the laser beam amplified in the laser resonator is delivered outside through the output mirror 8.
As shown in FIG. 6, assuming that magnetron 1, waveguide 2 and power source 4 to be one microwave generating unit (hereinafter called MGU) 200, plural MGUs 200 are used in one discharge tube 3. Further assuming the one discharge tube 3 and a plurality of MGUs 200 compose one microwave output unit (hereinafter called MOU) 300, the number of MOUs used in one MEGLO is determined by the laser output of the MEGLO.
FIG. 7 shows an example of using four MGUs 200 in one discharge tube 3, in which four microwave output timings are shown simultaneously. As shown in FIG. 7, each MGU 200 outputs intermittently so as to issue a microwave for a period of Ton 101, and cut off for a period of Toff 102. The microwave output timings from four MGUs 200 are nearly simultaneous. In order to stabilize the microwave output, pulse-width modulation (hereinafter called PWM) control of a specific off time is effected.
In the conventional MEGLO, the output of each magnetron 1 is controlled at a specific off time by the PWM control. However, when plural MGUs 200 composing one MOU 300 are disposed closely, the microwave output of each MGU 200 is issued at the same timing as shown in FIG. 7, and the discharges in the discharge area 10 may interfere with each other. In the event of such phenomenon, the continuous output of laser beam contains ripples, and the peak output of the laser beam in pulse operation fluctuates greatly, while at the same time, the laser beam output decreases. These problems are associated with the conventional MEGLO.